Sherlock was reluctant to call Mycroft 'brother' only because being created from the same nightmare was not the same as being born.
Slender men knew what they were, knew what each other were, but if they happened to cross each other's paths in between the folds of dream and wake, they would simply acknowledge the other's presence with a fleeting glance.
Mycroft- a name Sherlock had bestowed upon him- did more than glance. He would stop, and watch the others as they work. He always took his sweet time with his child, taking so much time many of his children grew into full fledged adults before he decided to take them.
And he was the only one who tolerated Sherlock's presence.
They both knew each other was unique and seemed to found a certain solace in that. But it was in the nature of horrors to be solitary creatures and they never stayed in each others' presence for long. The last time Sherlock saw his 'brother,' it was in 1645. It was a scrumptious year as there were many children abandoned by their parents in the height of the witch hunts. Some were even willing to be taken, better with a nightmare than facing a world of disease, torture and false truths.
Mycroft said nothing to him, the necessity of speech long forgone. Instead, he reached out and dragged one hand across Sherlock's chest.
Sherlock had never been touched, and was startled by the sudden pressure on his torso. He'd nearly leapt back in alarm, unsure if the caress was a threat. There was no such thing as fighting among them.
There was such thing as touching.
Mycroft pulled his hand away, giving no explanation why he did what he did.
Without another look, he stepped into the shadows, along with the children he had harvested, and disappeared.
The next time Sherlock saw him, nearly four hundred years later, Mycroft had but one child in his hand.
A boy. With blonde hair and a chubby face. It was not unusual for slender men to have preferences in their children, what was unusual that this boy was very much alive.
Mycroft has taken nothing from him. Not the boy's laughter, his tears, his sight, or his essence. He was untouched as the day he was born, his soul bright and full of life.
Mycroft stepped forward. Sherlock nearly leapt back, his hands going up, expecting another confrontation. Mycroft was acting too weird, even for Sherlock's own tastes.
The child, so warm and small, was suddenly dropped into Sherlock's outstretched hands.
Immediately Sherlock had to refrain from sucking the child dry. He had not eaten properly in years and the child's blood was a temptation too much. He slowly twisted the body in his hands, unsure how to distribute the weight, if the head was supported in the right way. The most he had ever taken from Greg or Sally was a dream, a hope, or a wish. Holding this unravished boy was like presenting a buffet to a starving man.
Sherlock nearly dropped the child in surprise as Mycroft's hand brushed against his chest again. As he pulled away, his finger brushed a lock of hair away from the child's face.
Mycroft then descended into the shadows, and Sherlock never saw him again.